medRxiv preprint doi: https://doi.org/10.1101/2021.06.07.21258522; this version posted June 12, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC 4.0 International license . 1 SARS-CoV-2 in wastewater from Mexico City used for irrigation in the Mezquital 2 Valley: quantification and modelling of geographic dispersion 3 4 Authors 5 Yaxk’in Coronado1, Roberto Navarro2, Carlos Mosqueda2,3, Valeria Valenzuela2,4, Juan 6 Pablo Perez2, VíCtor González-Mendoza1, Mayra de la Torre2, Jorge Rocha1*. 7 8 1ConaCyt-Unidad Regional Hidalgo, Centro de InvestigaCión en AlimentaCión y Desarrollo. 9 Ciudad del Conocimiento y la Cultura de Hidalgo, Blvd. Santa Catarina S/N, San Agustín 10 TlaxiaCa, Hidalgo, MéxiCo, 42163 11 2Unidad Regional Hidalgo. Centro de InvestigaCión en AlimentaCión y Desarrollo. Ciudad 12 del Conocimiento y la Cultura de Hidalgo, Blvd. Santa Catarina S/N, San Agustín TlaxiaCa, 13 Hidalgo, MéxiCo, 42163. 14 3Instituto TeCnológiCo de Celaya. Antonio García Cubas 600, Fovissste, Celaya, Gto., 15 38010. 16 4Universidad TeCnológiCa de Querétaro. Av. Pie de la Cuesta 2501, NaCional, Santiago de 17 Querétaro, Qro., 76148. 18 *Corresponding author: [email protected] 19 Additional data: 20 https://nbviewer.jupyter.org/github/yaxastro3000/COVID_CIAD_URH/blob/C65aC45af147 21 36023e94eb087aea8d541a7daC68/MODEL_COVID_CIAD_URH.ipynb 22 NOTE: This preprint reports new research that has not been certified by peer review and should not be used to guide clinical practice. medRxiv preprint doi: https://doi.org/10.1101/2021.06.07.21258522; this version posted June 12, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC 4.0 International license . 23 Abstract 24 QuantifiCation of SARS-CoV-2 in urban wastewaters has emerged as a cheap, effiCient 25 strategy to follow trends of aCtive COVID-19 cases in populations. Moreover, 26 mathematiCal models have been developed that allow prediCtion of aCtive cases following 27 the temporal patterns of viral loads in wastewaters. In MexiCo, no systematiC efforts have 28 been reported in the use of this strategies. In this work, we quantified SARS-CoV-2 in 29 rivers and irrigation canals in the Mezquital Valley, Hidalgo, an agriCultural region where 30 wastewater from MexiCo City is distributed and used for irrigation. Using quantitative RT- 31 PCR, we deteCted the virus in 6 out of 8 water samples from rivers, and 5 out of 8 water 32 samples from irrigation canals. Notably, samples showed a general consistent trend of 33 having the highest viral loads in the sites closer to MexiCo City, indiCating that this is the 34 main source that contributes to deteCtion. Using the data for SARS-CoV-2 concentration in 35 the river samples, we generated a simplified transport model that desCribes the spatial 36 patterns of dispersion of virus in the river. We suggest that this model can be extrapolated 37 to other wastewater systems that require knowledge of spatial patterns of viral dispersion at 38 a geographiC sCale. Our work highlights the need for improved praCtiCes and poliCies 39 related to the use of wastewater for irrigation in MexiCo and other countries. 40 Introduction 41 The ongoing global pandemiC of COVID-19 disease, caused by severe aCute respiratory 42 syndrome coronavirus 2 (SARS-CoV-2), is a publiC health emergency of international 43 Concern (Organization and Fund (UNICEF), 2020a, 2020b). SARS-CoV-2 ribonucleiC aCid 44 (RNA) has been deteCted in feCes from both symptomatiC and asymptomatiC patients (Chen 45 et al., 2020; Holshue et al., 2020; Jiehao et al., 2020; Tang et al., 2020; W. Wang et al., 46 2020; Zhang et al., 2020) and in wastewater (Ahmed et al., 2020; Lodder and Husman, 47 2020; Medema et al., 2020). For this reason, quantifiCation of SARS-CoV-2 ARN in 48 wastewater has emerged as a cheap, effiCient method for monitoring aCtive cases in large 49 populations (Ahmed et al., 2020; S. Wang et al., 2020), small towns (Kitajima et al., 2020; 50 Randazzo et al., 2020), or campuses (Harris-Lovett et al., 2021). Notably, this strategy 51 allows for a one-week antiCipation in the aCtive cases, compared to health systems medRxiv preprint doi: https://doi.org/10.1101/2021.06.07.21258522; this version posted June 12, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC 4.0 International license . 52 registries, since asymptomatiC individuals contribute to the viral load in wastewaters 53 (Vallejo et al., 2020; Wu et al., 2020). 54 MexiCo City has more than 661,446 confirmed cases of COVID-19 (MexiCo City 55 Government, 2020; consulted on June 1st, 2021); this is the city with the highest number of 56 Cases in the country. In Hidalgo, a state north of MexiCan Valley Metropolitan Area 57 (MVMA, Figure 1a), more than 39,012 positive cases have aCCumulated (State of Hidalgo 58 Government, 2021), of whiCh more than 11,000 cases (28%) correspond to the Mezquital 59 Valley, a highly productive agriCultural region. 60 To date, few systematiC efforts have been made in MexiCo to deteCt SARS-CoV-2 in 61 wastewater. However, the Mezquital Valley has several relevant charaCteristiCs for the 62 study of SARS-CoV-2 in wastewater: 1) agriCulture production is maintained by using 63 exclusively wastewater for irrigation (Contreras et al., 2017); 2) the wastewater source is 64 the MVMA, the most populated metropolitan area worldwide, and the region that 65 Concentrates most aCtive cases in MexiCo (Figure 1b) (Información referente a casos 66 COVID-19 en México - datos.gob.mx/busca); 3) the system includes one of the largest 67 wastewater treatment faCilities in Latin AmeriCa, whiCh feeds a river and a complex system 68 of irrigation canals; 4) farmers, inhabitants and consumers in the Mezquital Valley are in 69 ContaCt with water, soil or agriCultural products and 5) the use of wastewater for irrigation 70 is one of the main causes that allowed that this Valley is no longer in extreme poverty 71 (García-Salazar and García-Salazar, 2019). 72 Using data for SARS-CoV-2 concentration in wastewater, several models have been 73 proposed for to find a correlation between the temporal patterns of viral concentration and 74 the number of aCtive COVID-19 cases (Hart and Halden, 2020b). Likewise, a previous 75 work presented the first model of spatial and temporal patterns of viral loads in seaway 76 systems, showing the dispersion of the virus in an urban region (Hart and Halden, 2020a). 77 However, models for spatial patterns of viral dispersion are needed in open waterbodies 78 that contain wastewater, in order to understand the virus transport and to identify the zones 79 with higher risk of infeCtion. 80 In this study we sampled water from the Tula River, Salado River and irrigation canals in 81 the Mezquital Valley, whiCh reCeive wastewater from MexiCo City, to assess the presence medRxiv preprint doi: https://doi.org/10.1101/2021.06.07.21258522; this version posted June 12, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC 4.0 International license . 82 of SARS-CoV-2 and generate a mathematiCal model that desCribes its spatial dispersion. 83 We propose that our results highly relevant not only to follow the epidemiC in MexiCo City 84 and muniCipalities in Hidalgo, but also to evaluate a possible risk of transmission through 85 environmental matriCes and measure the stability of SARS-CoV-2 with geographiC 86 resolution. 87 Materials and Methods 88 Sampling. Water samples were taken along the Tula River between the mouth of the 89 Central Interceptor Tunnel and Ixmiquilpan; samples were also taken in the Salado River, 90 whiCh reCeives wastewater from the Grand Drainage Canal, and Tepeji river, whiCh 91 Contains wastewaters from local muniCipalities (Figure 1). We also colleCted water samples 92 from irrigation canals in locations representative of the Mezquital Valley. Appropriate 93 safety equipment was always used, consisting of a cotton lab coat, latex gloves, KN95 94 respirator-mask, rubber boots, disposable cap, and safety glasses. A simple sampling 95 teChnique was used (NOM, 1980; EPA, 2017), locating sites where the wastewater is well 96 mixed near to the center of the flow channel, approximately between 40 and 60 percent of 97 water depth, where turbulence is maximum, and there is minimum sedimentation of solids. 98 For eaCh location, three water samples were colleCted as follows: two samples of 400 ml in 99 glass bottles, for SARS-CoV-2 deteCtion and for miCrobiologiCal analyses; and one 4 L 100 sample in a plastiC bottle, for physiCochemiCal analysis. For eaCh water sample colleCted at 101 an irrigation canal, we sampled 500 g of soil from an adjaCent agriCultural field. All 102 samples were immediately plaCed in iCe until arrival at the laboratory. Water samples for 103 SARS-CoV-2 deteCtion were inaCtivated by incubation at 60˚C for 1 h upon arrival at the 104 laboratory. 105 Physicochemical and Microbiological Analyses. Samples for physiCochemiCal and 106 miCrobiologiCal analyses were stored in iCe from sampling until delivery to external 107 laboratories where determinations were carried out.